Method for forming three-dimensional memory device with backside source contact

ABSTRACT

Embodiments of 3D memory devices and methods for forming the same are disclosed. In an example, a method for forming a 3D memory device is disclosed. A sacrificial layer above a second semiconductor layer at a first side of a substrate and a dielectric stack on the sacrificial layer are subsequently formed. A channel structure extending vertically through the dielectric stack and the sacrificial layer into the second semiconductor layer is formed. The sacrificial layer is replaced with a first semiconductor layer in contact with the second semiconductor layer. The dielectric stack is replaced with a memory stack, such that the channel structure extends vertically through the memory stack and the first semiconductor layer into the second semiconductor layer. A source contact is formed at a second side opposite to the first side of the substrate to be in contact with the second semiconductor layer.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of International Application No.PCT/CN2020/084603, filed on Apr. 14, 2020, entitled “METHOD FOR FORMINGTHREE-DIMENSIONAL MEMORY DEVICE WITH BACKSIDE SOURCE CONTACT,” which ishereby incorporated by reference in its entirety. This application isalso related to U.S. application Ser. No. 16/881,294, filed on May 22,2020, entitled “THREE-DIMENSIONAL MEMORY DEVICE WITH BACKSIDE SOURCECONTACT,” which is hereby incorporated by reference in its entirety.

BACKGROUND

Embodiments of the present disclosure relate to three-dimensional (3D)memory devices and fabrication methods thereof.

Planar memory cells are scaled to smaller sizes by improving processtechnology, circuit design, programming algorithm, and fabricationprocess. However, as feature sizes of the memory cells approach a lowerlimit, planar process and fabrication techniques become challenging andcostly. As a result, memory density for planar memory cells approachesan upper limit.

A 3D memory architecture can address the density limitation in planarmemory cells. The 3D memory architecture includes a memory array andperipheral devices for controlling signals to and from the memory array.

SUMMARY

Embodiments of 3D memory devices and methods for forming the same aredisclosed herein.

In one example, a method for forming a 3D memory device is disclosed. Asacrificial layer above a second semiconductor layer at a first side ofa substrate and a dielectric stack on the sacrificial layer aresubsequently formed. A channel structure extending vertically throughthe dielectric stack and the sacrificial layer into the secondsemiconductor layer is formed. The sacrificial layer is replaced with afirst semiconductor layer in contact with the second semiconductorlayer. The dielectric stack is replaced with a memory stack, such thatthe channel structure extends vertically through the memory stack andthe first semiconductor layer into the second semiconductor layer. Asource contact is formed at a second side opposite to the first side ofthe substrate to be in contact with the second semiconductor layer.

In another example, a method for forming a 3D memory device isdisclosed. A channel structure extending vertically through a memorystack into an N-type doped semiconductor layer at a first side of asubstrate is formed. The memory stack includes interleaved stackconductive layers and stack dielectric layers. An insulating structureis formed in an opening extending vertically through the memory stack. Asource contact is formed at a second side opposite to the first side ofthe substrate to be in contact with the N-type doped semiconductor layerand aligned with the insulating structure.

In still another example, a method for forming a 3D memory device isdisclosed. A peripheral circuit is formed on a first substrate. Achannel structure extending vertically through a memory stack and afirst semiconductor layer into a second semiconductor layer on a secondsubstrate is formed. The first substrate and the second substrate arebonded in a face-to-face manner, such that the memory stack is above theperipheral circuit. The second substrate is thinned to expose the secondsemiconductor layer. A source contact is formed above the memory stackand in contact with the second semiconductor layer.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated herein and form a partof the specification, illustrate embodiments of the present disclosureand, together with the description, further serve to explain theprinciples of the present disclosure and to enable a person skilled inthe pertinent art to make and use the present disclosure.

FIG. 1 illustrates a side view of a cross-section of an exemplary 3Dmemory device with a backside source contact, according to someembodiments of the present disclosure.

FIG. 2A illustrates a plan view of a cross-section of an exemplary 3Dmemory device with a backside source contact, according to someembodiments of the present disclosure.

FIG. 2B illustrates another plan view of a cross-section of an exemplary3D memory device with a backside source contact, according to someembodiments of the present disclosure.

FIGS. 3A-3M illustrate a fabrication process for forming an exemplary 3Dmemory device with a backside source contact, according to someembodiments of the present disclosure.

FIGS. 4A and 4B illustrate a flowchart of a method for forming anexemplary 3D memory device with a backside source contact, according tosome embodiments of the present disclosure.

Embodiments of the present disclosure will be described with referenceto the accompanying drawings.

DETAILED DESCRIPTION

Although specific configurations and arrangements are discussed, itshould be understood that this is done for illustrative purposes only. Aperson skilled in the pertinent art will recognize that otherconfigurations and arrangements can be used without departing from thespirit and scope of the present disclosure. It will be apparent to aperson skilled in the pertinent art that the present disclosure can alsobe employed in a variety of other applications.

It is noted that references in the specification to “one embodiment,”“an embodiment,” “an example embodiment,” “some embodiments,” etc.,indicate that the embodiment described may include a particular feature,structure, or characteristic, but every embodiment may not necessarilyinclude the particular feature, structure, or characteristic. Moreover,such phrases do not necessarily refer to the same embodiment. Further,when a particular feature, structure or characteristic is described inconnection with an embodiment, it would be within the knowledge of aperson skilled in the pertinent art to effect such feature, structure orcharacteristic in connection with other embodiments whether or notexplicitly described.

In general, terminology may be understood at least in part from usage incontext. For example, the term “one or more” as used herein, dependingat least in part upon context, may be used to describe any feature,structure, or characteristic in a singular sense or may be used todescribe combinations of features, structures or characteristics in aplural sense. Similarly, terms, such as “a,” “an,” or “the,” again, maybe understood to convey a singular usage or to convey a plural usage,depending at least in part upon context. In addition, the term “basedon” may be understood as not necessarily intended to convey an exclusiveset of factors and may, instead, allow for existence of additionalfactors not necessarily expressly described, again, depending at leastin part on context.

It should be readily understood that the meaning of “on,” “above,” and“over” in the present disclosure should be interpreted in the broadestmanner such that “on” not only means “directly on” something but alsoincludes the meaning of “on” something with an intermediate feature or alayer therebetween, and that “above” or “over” not only means themeaning of “above” or “over” something but can also include the meaningit is “above” or “over” something with no intermediate feature or layertherebetween (i.e., directly on something).

Further, spatially relative terms, such as “beneath,” “below,” “lower,”“above,” “upper,” and the like, may be used herein for ease ofdescription to describe one element or feature's relationship to anotherelement(s) or feature(s) as illustrated in the figures. The spatiallyrelative terms are intended to encompass different orientations of thedevice in use or operation in addition to the orientation depicted inthe figures. The apparatus may be otherwise oriented (rotated 90 degreesor at other orientations) and the spatially relative descriptors usedherein may likewise be interpreted accordingly.

As used herein, the term “substrate” refers to a material onto whichsubsequent material layers are added. The substrate itself can bepatterned. Materials added on top of the substrate can be patterned orcan remain unpatterned. Furthermore, the substrate can include a widearray of semiconductor materials, such as silicon, germanium, galliumarsenide, indium phosphide, etc. Alternatively, the substrate can bemade from an electrically non-conductive material, such as a glass, aplastic, or a sapphire wafer.

As used herein, the term “layer” refers to a material portion includinga region with a thickness. A layer can extend over the entirety of anunderlying or overlying structure or may have an extent less than theextent of an underlying or overlying structure. Further, a layer can bea region of a homogeneous or inhomogeneous continuous structure that hasa thickness less than the thickness of the continuous structure. Forexample, a layer can be located between any pair of horizontal planesbetween, or at, a top surface and a bottom surface of the continuousstructure. A layer can extend horizontally, vertically, and/or along atapered surface. A substrate can be a layer, can include one or morelayers therein, and/or can have one or more layer thereupon, thereabove,and/or therebelow. A layer can include multiple layers. For example, aninterconnect layer can include one or more conductor and contact layers(in which interconnect lines and/or vertical interconnect access (via)contacts are formed) and one or more dielectric layers.

As used herein, the term “nominal/nominally” refers to a desired, ortarget, value of a characteristic or parameter for a component or aprocess operation, set during the design phase of a product or aprocess, together with a range of values above and/or below the desiredvalue. The range of values can be due to slight variations inmanufacturing processes or tolerances. As used herein, the term “about”indicates the value of a given quantity that can vary based on aparticular technology node associated with the subject semiconductordevice. Based on the particular technology node, the term “about” canindicate a value of a given quantity that varies within, for example,10-30% of the value (e.g., ±10%, ±20%, or ±30% of the value).

As used herein, the term “3D memory device” refers to a semiconductordevice with vertically oriented strings of memory cell transistors(referred to herein as “memory strings,” such as NAND memory strings) ona laterally-oriented substrate so that the memory strings extend in thevertical direction with respect to the substrate. As used herein, theterm “vertical/vertically” means nominally perpendicular to the lateralsurface of a substrate.

In some 3D memory devices, such as 3D NAND memory devices, slitstructures (e.g., gate line slits (GLSs)) are used for providingelectrical connections to the source of the memory array, such as arraycommon source (ACS), from the front side of the devices. The front sidesource contacts, however, can affect the electrical performance of the3D memory devices by introducing both leakage current and parasiticcapacitance between the word lines and the source contacts, even withthe presence of spacers in between. The formation of the spacers alsocomplicates the fabrication process. Besides affecting the electricalperformance, the slit structures usually include wall-shaped polysiliconand/or metal fillings, which can introduce local stress to cause waferbow or warp, thereby reducing the production yield.

Moreover, some 3D NAND memory devices include semiconductor plugsselectively grown at the bottom of the channel structures. However, asthe number of levels of 3D NAND memory devices increases, in particular,with multi-deck architecture, various issues are involved in thefabrication of the bottom semiconductor plugs, such as overlay control,epitaxial layer formation, and etching of memory film and semiconductorchannel at the bottom of the channel holes (also known as “SONO punch”),which further complicates the fabrication process and may reduce theyield.

Various embodiments in accordance with the present disclosure provide 3Dmemory devices with backside source contacts. By moving the sourcecontacts from the front side to the backside, the cost per memory cellcan be reduced as the effective memory cell array area can be increasedand the spacers formation process can be skipped. The device performancecan be improved as well, for example, by avoiding the leakage currentand parasitic capacitance between the word lines and the source contactsand by reducing the local stress caused by the front side slitstructures (as source contacts). In some embodiments, the 3D memorydevices do not include semiconductor plugs selectively grown at thebottom of the channel structures, which are replaced by semiconductorlayers (e.g., N-wells) surrounding the sidewalls of the channelstructures, which can enable gate-induce-drain-leakage (GIDL)-assistedbody biasing for erase operations. As a result, various issuesassociated with the bottom semiconductor plugs can be avoided, such asoverlay control, epitaxial layer formation, and SONO punch, therebyincreasing the production yield.

FIG. 1 illustrates a side view of a cross-section of an exemplary 3Dmemory device 100 with a backside source contact, according to someembodiments of the present disclosure. In some embodiments, 3D memorydevice 100 is a bonded chip including a first semiconductor structure102 and a second semiconductor structure 104 stacked over firstsemiconductor structure 102. First and second semiconductor structures102 and 104 are jointed at a bonding interface 106 therebetween,according to some embodiments. As shown in FIG. 1 , first semiconductorstructure 102 can include a substrate 101, which can include silicon(e.g., single crystalline silicon, c-Si), silicon germanium (SiGe),gallium arsenide (GaAs), germanium (Ge), silicon on insulator (SOI), orany other suitable materials.

First semiconductor structure 102 of 3D memory device 100 can includeperipheral circuits 108 on substrate 101. It is noted that x-, y-, andz-axes are included in FIG. 1 to illustrate the spatial relationships ofthe components in 3D memory device 100. Substrate 101 includes twolateral surfaces extending laterally in the x-y plane: a front surfaceon the front side of the wafer, and a back surface on the backsideopposite to the front side of the wafer. The x- and y-directions are twoorthogonal directions in the wafer plane: x-direction is the word linedirection, and the y-direction is the bit line direction. The z-axis isperpendicular to both the x- and y-axes. As used herein, whether onecomponent (e.g., a layer or a device) is “on,” “above,” or “below”another component (e.g., a layer or a device) of a semiconductor device(e.g., 3D memory device 100) is determined relative to the substrate ofthe semiconductor device (e.g., substrate 101) in the z-direction (thevertical direction perpendicular to the x-y plane) when the substrate ispositioned in the lowest plane of the semiconductor device in thez-direction. The same notion for describing spatial relationships isapplied throughout the present disclosure.

In some embodiments, peripheral circuit 108 is configured to control andsense the 3D memory device 100. Peripheral circuit 108 can be anysuitable digital, analog, and/or mixed-signal control and sensingcircuits used for facilitating the operation of 3D memory device 100including, but not limited to, a page buffer, a decoder (e.g., a rowdecoder and a column decoder), a sense amplifier, a driver (e.g., a wordline driver), a charge pump, a current or voltage reference, or anyactive or passive components of the circuit (e.g., transistors, diodes,resistors, or capacitors). Peripheral circuits 108 can includetransistors formed “on” substrate 101, in which the entirety or part ofthe transistors are formed in substrate 101 (e.g., below the top surfaceof substrate 101) and/or directly on substrate 101. Isolation regions(e.g., shallow trench isolations (STIs)) and doped regions (e.g., sourceregions and drain regions of the transistors) can be formed in substrate101 as well. The transistors are high-speed with advanced logicprocesses (e.g., technology nodes of 90 nm, 65 nm, 45 nm, 32 nm, 28 nm,20 nm, 16 nm, 14 nm, 10 nm, 7 nm, 5 nm, 3 nm, etc.), according to someembodiments. It is understood that in some embodiments, peripheralcircuit 108 may further include any other circuits compatible with theadvanced logic processes including logic circuits, such as processorsand programmable logic devices (PLDs), or memory circuits, such asstatic random-access memory (SRAM).

In some embodiments, first semiconductor structure 102 of 3D memorydevice 100 further includes an interconnect layer (not shown) aboveperipheral circuits 108 to transfer electrical signals to and fromperipheral circuits 108. The interconnect layer can include a pluralityof interconnects (also referred to herein as “contacts”), includinglateral interconnect lines and vertical interconnect access (VIA)contacts. As used herein, the term “interconnects” can broadly includeany suitable types of interconnects, such as middle-end-of-line (MEOL)interconnects and back-end-of-line (BEOL) interconnects. Theinterconnect layer can further include one or more interlayer dielectric(ILD) layers (also known as “intermetal dielectric (IMD) layers”) inwhich the interconnect lines and VIA contacts can form. That is, theinterconnect layer can include interconnect lines and VIA contacts inmultiple ILD layers. The interconnect lines and VIA contacts in theinterconnect layer can include conductive materials including, but notlimited to, tungsten (W), cobalt (Co), copper (Cu), aluminum (Al),silicides, or any combination thereof. The ILD layers in theinterconnect layer can include dielectric materials including, but notlimited to, silicon oxide, silicon nitride, silicon oxynitride, lowdielectric constant (low-k) dielectrics, or any combination thereof.

As shown in FIG. 1 , first semiconductor structure 102 of 3D memorydevice 100 can further include a bonding layer 110 at bonding interface106 and above the interconnect layer and peripheral circuits 108.Bonding layer 110 can include a plurality of bonding contacts 111 anddielectrics electrically isolating bonding contacts 111. Bondingcontacts 111 can include conductive materials including, but not limitedto, W, Co, Cu, Al, silicides, or any combination thereof. The remainingarea of bonding layer 110 can be formed with dielectrics including, butnot limited to, silicon oxide, silicon nitride, silicon oxynitride,low-k dielectrics, or any combination thereof. Bonding contacts 111 andsurrounding dielectrics in bonding layer 110 can be used for hybridbonding.

Similarly, as shown in FIG. 1 , second semiconductor structure 104 of 3Dmemory device 100 can also include a bonding layer 112 at bondinginterface 106 and above bonding layer 110 of first semiconductorstructure 102. Bonding layer 112 can include a plurality of bondingcontacts 113 and dielectrics electrically isolating bonding contacts113. Bonding contacts 113 can include conductive materials including,but not limited to, W, Co, Cu, Al, silicides, or any combinationthereof. The remaining area of bonding layer 112 can be formed withdielectrics including, but not limited to, silicon oxide, siliconnitride, silicon oxynitride, low-k dielectrics, or any combinationthereof. Bonding contacts 113 and surrounding dielectrics in bondinglayer 112 can be used for hybrid bonding. Bonding contacts 113 are incontact with bonding contacts 111 at bonding interface 106, according tosome embodiments.

As described below in detail, second semiconductor structure 104 can bebonded on top of first semiconductor structure 102 in a face-to-facemanner at bonding interface 106. In some embodiments, bonding interface106 is disposed between bonding layers 110 and 112 as a result of hybridbonding (also known as “metal/dielectric hybrid bonding”), which is adirect bonding technology (e.g., forming bonding between surfaceswithout using intermediate layers, such as solder or adhesives) and canobtain metal-metal bonding and dielectric-dielectric bondingsimultaneously. In some embodiments, bonding interface 106 is the placeat which bonding layers 112 and 110 are met and bonded. In practice,bonding interface 106 can be a layer with a certain thickness thatincludes the top surface of bonding layer 110 of first semiconductorstructure 102 and the bottom surface of bonding layer 112 of secondsemiconductor structure 104.

In some embodiments, second semiconductor structure 104 of 3D memorydevice 100 further includes an interconnect layer (not shown) abovebonding layer 112 to transfer electrical signals. The interconnect layercan include a plurality of interconnects, such as MEOL interconnects andBEOL interconnects. The interconnect layer can further include one ormore ILD layers in which the interconnect lines and VIA contacts canform. The interconnect lines and VIA contacts in the interconnect layercan include conductive materials including, but not limited to W, Co,Cu, Al, silicides, or any combination thereof. The ILD layers in theinterconnect layer can include dielectric materials including, but notlimited to, silicon oxide, silicon nitride, silicon oxynitride, low-kdielectrics, or any combination thereof.

In some embodiments, 3D memory device 100 is a NAND Flash memory devicein which memory cells are provided in the form of an array of NANDmemory strings. As shown in FIG. 1 , second semiconductor structure 104of 3D memory device 100 can include an array of channel structures 124functioning as the array of NAND memory strings. As shown in FIG. 1 ,each channel structure 124 can extend vertically through a plurality ofpairs each including a conductive layer 116 and a dielectric layer 118.The interleaved conductive layers 116 and dielectric layers 118 are partof a memory stack 114. The number of the pairs of conductive layers 116and dielectric layers 118 in memory stack 114 (e.g., 32, 64, 96, 128,160, 192, 224, 256, or more) determines the number of memory cells in 3Dmemory device 100. It is understood that in some embodiments, memorystack 114 may have a multi-deck architecture (not shown), which includesa plurality of memory decks stacked over one another. The numbers of thepairs of conductive layers 116 and dielectric layers 118 in each memorydeck can be the same or different.

Memory stack 114 can include a plurality of interleaved conductivelayers 116 and dielectric layers 118. Conductive layers 116 anddielectric layers 118 in memory stack 114 can alternate in the verticaldirection. In other words, except the ones at the top or bottom ofmemory stack 114, each conductive layer 116 can be adjoined by twodielectric layers 118 on both sides, and each dielectric layer 118 canbe adjoined by two conductive layers 116 on both sides. Conductivelayers 116 can include conductive materials including, but not limitedto, W, Co, Cu, Al, polysilicon, doped silicon, silicides, or anycombination thereof. Each conductive layer 116 can include a gateelectrode (gate line) surrounded by an adhesive layer and a gatedielectric layer. The gate electrode of conductive layer 116 can extendlaterally as a word line, ending at one or more staircase structures ofmemory stack 114. Dielectric layers 118 can include dielectric materialsincluding, but not limited to, silicon oxide, silicon nitride, siliconoxynitride, or any combination thereof.

As shown in FIG. 1 , second semiconductor structure 104 of 3D memorydevice 100 can also include a first semiconductor layer 120 above memorystack 114 and a second semiconductor layer 122 above and in contact withfirst semiconductor layer 120. In some embodiments, each of first andsecond semiconductor layers 120 and 122 is an N-type doped semiconductorlayer, e.g., a silicon layer doped with N-type dopant(s), such asphosphorus (P) or arsenic (As). In those cases, first and secondsemiconductor layers 120 and 122 may be viewed collectively as an N-typedoped semiconductor layer 120/122 above memory stack 114. In someembodiments, each of first and second semiconductor layers 120 and 122includes an N-well. That is, each of first and second semiconductorlayers 120 and 122 can be a region in a P-type substrate that is dopedwith N-type dopant(s), such as P or As. It is understood that the dopingconcentrations in first and second semiconductor layers 120 and 122 maybe the same or different. First semiconductor layer 120 includespolysilicon, for example, N-type doped polysilicon, according to someembodiments. As described below in detail, first semiconductor layer 120can be formed above a P-type silicon substrate by thin film depositionand/or epitaxial growth. In contrast, second semiconductor layer 122includes single crystalline silicon, for example, N-type doped singlecrystalline silicon, according to some embodiments. As described belowin detail, second semiconductor layer 122 can be formed by implantingN-type dopant(s) into a P-type silicon substrate having singlecrystalline silicon. In some embodiments, the lateral dimension ofsecond semiconductor layer 122 in the x-direction (e.g., the word linedirection) is greater than the lateral dimension of first semiconductorlayer 120 in the x-direction.

In some embodiments, each channel structure 124 includes a channel holefilled with a semiconductor layer (e.g., as a semiconductor channel 128)and a composite dielectric layer (e.g., as a memory film 126). In someembodiments, semiconductor channel 128 includes silicon, such asamorphous silicon, polysilicon, or single crystalline silicon. In someembodiments, memory film 126 is a composite layer including a tunnelinglayer, a storage layer (also known as a “charge trap layer”), and ablocking layer. The remaining space of channel structure 124 can bepartially or fully filled with a capping layer including dielectricmaterials, such as silicon oxide, and/or an air gap. Channel structure124 can have a cylinder shape (e.g., a pillar shape). The capping layer,semiconductor channel 128, the tunneling layer, storage layer, andblocking layer of memory film 126 are arranged radially from the centertoward the outer surface of the pillar in this order, according to someembodiments. The tunneling layer can include silicon oxide, siliconoxynitride, or any combination thereof. The storage layer can includesilicon nitride, silicon oxynitride, silicon, or any combinationthereof. The blocking layer can include silicon oxide, siliconoxynitride, high-k dielectrics, or any combination thereof. In oneexample, memory film 126 can include a composite layer of siliconoxide/silicon oxynitride/silicon oxide (ONO).

In some embodiments, channel structure 124 further includes a channelplug 129 in the bottom portion (e.g., at the lower end) of channelstructure 124. As used herein, the “upper end” of a component (e.g.,channel structure 124) is the end farther away from substrate 101 in thez-direction, and the “lower end” of the component (e.g., channelstructure 124) is the end closer to substrate 101 in the z-directionwhen substrate 101 is positioned in the lowest plane of 3D memory device100. Channel plug 129 can include semiconductor materials (e.g.,polysilicon). In some embodiments, channel plug 129 functions as thedrain of the NAND memory string.

As shown in FIG. 1 , each channel structure 124 can extend verticallythrough interleaved conductive layers 116 and dielectric layers 118 ofmemory stack 114 and first semiconductor layer 120, e.g., an N-typedoped polysilicon layer. In some embodiments, first semiconductor layer120 surrounds part of channel structure 124 and is in contact withsemiconductor channel 128 including polysilicon. That is, memory film126 is disconnected at part of channel structure 124 that abuts firstsemiconductor layer 120, exposing semiconductor channel 128 to be incontact with the surrounding first semiconductor layer 120, according tosome embodiments. As a result, first semiconductor layer 120 surroundingand in contact with semiconductor channel 128 can work as a “sidewallsemiconductor plug” of channel structure 124 to replace the “bottomsemiconductor plug” as described above, which can mitigate issues suchas overlay control, epitaxial layer formation, and SONO punch.

In some embodiments, each channel structure 124 can extend verticallyfurther into second semiconductor layer 122, e.g., an N-type dopedsingle crystalline silicon layer. That is, each channel structure 124extends vertically through memory stack 114 into the N-type dopedsemiconductor layer (including first and second semiconductor layers 120and 122), according to some embodiments. As shown in FIG. 1 , the topportion (e.g., the upper end) of channel structures 124 is in secondsemiconductor layer 122, according to some embodiments. In someembodiments, each of first and second semiconductor layers 120 and 122is an N-type doped semiconductor layer, e.g., an N-well, to enableGIDL-assisted body biasing for erase operations, as opposed to P-wellbulk erase operations. The GIDL around the source select gate of theNAND memory string can generate hole current into the NAND memory stringto raise the body potential for erase operations.

As shown in FIG. 1 , second semiconductor structure 104 of 3D memorydevice 100 can further include insulating structures 130 each extendingvertically through interleaved conductive layers 116 and dielectriclayers 118 of memory stack 114. Different from channel structure 124that extends further through first semiconductor layer 120, insulatingstructures 130 stops at first semiconductor layer 120, i.e., does notextend vertically into the N-type doped semiconductor layer, accordingto some embodiments. That is, the top surface of insulating structure130 can be flush with the bottom surface of first semiconductor layer120. Each insulating structure 130 can also extend laterally to separatechannel structures 124 into a plurality of blocks. That is, memory stack114 can be divided into a plurality of memory blocks by insulatingstructures 130, such that the array of channel structures 124 can beseparated into each memory block. Different from the slit structures inexisting 3D NAND memory devices described above, which include frontside ACS contacts, insulating structure 130 does not include any contacttherein (i.e., not functioning as the source contact) and thus, does notintroduce parasitic capacitance and leakage current with conductivelayers 116 (including word lines), according to some embodiments. Insome embodiments, each insulating structure 130 includes an opening(e.g., a slit) filled with one or more dielectric materials, including,but not limited to, silicon oxide, silicon nitride, silicon oxynitride,or any combination thereof. In one example, each insulating structure130 may be filled with silicon oxide.

Instead of the front side source contacts, 3D memory device 100 caninclude a backside source contact 132 above memory stack 114 and incontact with second semiconductor layer 122, e.g., the N-type dopedsemiconductor layer, as shown in FIG. 1 . Source contact 132 and memorystack 114 (and insulating structure 130 therethrough) can be disposed atopposites sides of semiconductor layer 122 (a thinned substrate) andthus, viewed as a “backside” source contact. In some embodiments, sourcecontact 132 extends further into second semiconductor layer 122 and iselectrically connected to first semiconductor layer 120 andsemiconductor channel 128 of channel structure 124 through secondsemiconductor layer 122. It is understood that the depth that sourcecontact 132 extends into second semiconductor layer 122 may vary indifferent examples. In some embodiments in which second semiconductorlayer 122 includes an N-well, source contact 132 is also referred toherein as an “N-well pick up.” In some embodiments, source contact 132is aligned with insulating structure 130. Source contact 132 can belaterally aligned with insulating structure 130, i.e., aligned in atleast one lateral direction. In one example, source contact 132 andinsulating structure 130 may be aligned in they-direction (e.g., the bitline direction). In another example, source contact 132 and insulatingstructure 130 may be aligned in the x-direction (e.g., the word linedirection). Source contacts 132 can include any suitable types ofcontacts. In some embodiments, source contacts 132 include a VIAcontact. In some embodiments, source contacts 132 include a wall-shapedcontact extending laterally. Source contact 132 can include one or moreconductive layers, such as a metal layer (e.g., W, Co, Cu, or Al) or asilicide layer surrounded by an adhesive layer (e.g., titanium nitride(TiN)).

As shown in FIG. 1 , 3D memory device 100 can further include a BEOLinterconnect layer 133 above and in contact with source contact 132 forpad-out, e.g., transferring electrical signals between 3D memory device100 and external circuits. In some embodiments, interconnect layer 133includes one or more ILD layers 134 on second semiconductor layer 122and a redistribution layer 136 on ILD layers 134. The upper end ofsource contact 132 is flush with the top surface of ILD layers 134 andthe bottom surface of redistribution layer 136, and source contact 132extends vertically through ILD layers 134 into second semiconductorlayer 122, according to some embodiments. ILD layers 134 in interconnectlayer 133 can include dielectric materials including, but not limitedto, silicon oxide, silicon nitride, silicon oxynitride, low-kdielectrics, or any combination thereof. Redistribution layer 136 ininterconnect layer 133 can include conductive materials including, butnot limited to W, Co, Cu, Al, silicides, or any combination thereof. Inone example, redistribution layer 136 includes Al. In some embodiments,interconnect layer 133 further includes a passivation layer 138 as theoutmost layer for passivation and protection of 3D memory device 100.Part of redistribution layer 136 can be exposed from passivation layer138 as contact pads 140. That is, interconnect layer 133 of 3D memorydevice 100 can also include contact pads 140 for wire bonding and/orbonding with an interposer.

In some embodiments, second semiconductor structure 104 of 3D memorydevice 100 further includes contacts 142 and 144 through secondsemiconductor layer 122. As second semiconductor layer 122 can be athinned substrate, for example, an N-well of a P-type silicon substrate,contacts 142 and 144 are through silicon contacts (TSCs), according tosome embodiments. In some embodiments, contact 142 extends throughsecond semiconductor layer 122 and ILD layers 134 to be in contact withredistribution layer 136, such that first semiconductor layer 120 iselectrically connected to contact 142 through second semiconductor layer122, source contact 132, and redistribution layer 136 of interconnectlayer 133. In some embodiments, contact 144 extends through secondsemiconductor layer 122 and ILD layers 134 to be in contact with contactpad 140. Contacts 142 and 144 each can include one or more conductivelayers, such as a metal layer (e.g., W, Co, Cu, or Al) or a silicidelayer surrounded by an adhesive layer (e.g., TiN). In some embodiments,at least contact 144 further includes a spacer (e.g., a dielectriclayer) to electrically insulate contact 144 from second semiconductorlayer 122.

In some embodiments, 3D memory device 100 further includes peripheralcontacts 146 and 148 each extending vertically to second semiconductorlayer 122 (e.g., an N-well of a P-type silicon substrate) outside ofmemory stack 114. Each peripheral contact 146 or 148 can have a depthgreater than the depth of memory stack 114 to extend vertically frombonding layer 112 to second semiconductor layer 122 in a peripheralregion that is outside of memory stack 114. In some embodiments,peripheral contact 146 is below and in contact with contact 142, suchthat first semiconductor layer 120 is electrically connected toperipheral circuit 108 in first semiconductor structure 102 through atleast second semiconductor layer 122, source contact 132, interconnectlayer 133, contact 142, and peripheral contact 146. In some embodiments,peripheral contact 148 is below and in contact with contact 144, suchthat peripheral circuit 108 in first semiconductor structure 102 iselectrically connected to contact pad 140 for pad-out through at leastcontact 144 and peripheral contact 148. Peripheral contacts 146 and 148each can include one or more conductive layers, such as a metal layer(e.g., W, Co, Cu, or Al) or a silicide layer surrounded by an adhesivelayer (e.g., TiN).

As shown in FIG. 1 , 3D memory device 100 also includes a variety oflocal contacts (also known as “C1”) as part of the interconnectstructure, which are in contact with a structure in memory stack 114directly. In some embodiments, the local contacts include channel localcontacts 150 each below and in contact with the lower end of arespective channel structure 124. Each channel local contact 150 can beelectrically connected to a bit line contact (not shown) for bit linefan-out. In some embodiments, the local contacts further include wordline local contacts 152 each below and in contact with a respectiveconductive layer 116 (including a word line) at the staircase structureof memory stack 114 for word line fan-out. Local contacts, such aschannel local contacts 150 and word line local contacts 152, can beelectrically connected to peripheral circuits 108 of first semiconductorstructure 102 through at least bonding layers 112 and 110. Localcontacts, such as channel local contacts 150 and word line localcontacts 152, each can include one or more conductive layers, such as ametal layer (e.g., W, Co, Cu, or Al) or a silicide layer surrounded byan adhesive layer (e.g., TiN).

FIG. 2A illustrates a plan view of a cross-section of an exemplary 3Dmemory device 200 with a backside source contact, according to someembodiments of the present disclosure. 3D memory device 200 may be oneexample of 3D memory device 100 in FIG. 1 , and FIG. 2A may illustrate aplan view of the cross-section in the AA plane of 3D memory device 100in FIG. 1 , according to some embodiments. That is, FIG. 2A shows oneexample of the plan view at the front side of second semiconductorstructure 104 of 3D memory device 100.

As shown in FIG. 2A, 3D memory device 200 includes a center staircaseregion 204 laterally separating the memory stack in the x-direction(e.g., the word line direction) into two parts: a first core arrayregion 206A and a second core array region 206B, each of which includesan array of channel structures 210 (corresponding to channel structures124 in FIG. 1 ), according to some embodiments. It is understood thatthe layout of the staircase region and core array regions is not limitedto the example of FIG. 2A and may include any other suitable layouts,such as having side staircase regions at the edges of the memory stack.3D memory device 200 also includes parallel insulating structures 208(corresponding to insulating structures 130 in FIG. 1 ) inthey-direction (e.g., the bit line direction) each extending laterallyin the x-direction to separate core array regions 206A and 206 andarrays of channel structures 210 therein into blocks 202, according tosome embodiments. 3D memory device 200 can further include paralleldrain select gate cuts 212 in the y-direction in block 202 to furtherseparate block 202 into fingers. Different from existing 3D memorydevices with front side source contacts disposed at the counterparts ofinsulating structures 208 (e.g., front side ACS contacts), whichinterrupt the front side bit line fan-out of certain channel structures210 (e.g., in regions 214), channel structure 210, including the ones inregions 214, in 3D memory device 200 without front side source contactscan all have corresponding bit lines fan-out from the front side. As aresult, the effective area of core array regions 206A and 206B can beincreased by moving the source contacts to the backside of 3D memorydevice 200.

FIG. 2B illustrates another plan view of a cross-section of an exemplary3D memory device with a backside source contact, according to someembodiments of the present disclosure. 3D memory device 200 may be oneexample of 3D memory device 100 in FIG. 1 , and FIG. 2B illustrates aplan view of the cross-section in the BB plane of 3D memory device 100in FIG. 1 , according to some embodiments. That is, FIG. 2B shows oneexample of the plan view at the backside of second semiconductorstructure 104 of 3D memory device 100.

As shown in FIG. 2B, 3D memory device 200 includes center staircaseregion 204 laterally separating the memory stack in the x-direction(e.g., the word line direction) into two parts: first core array region206A and second core array region 206B. It is understood that the layoutof the staircase region and core array regions is not limited to theexample of FIG. 2B and may include any other suitable layouts, such ashaving side staircase regions at the edges of the memory stack. In someembodiments, 3D memory device 200 includes backside source contacts 215(e.g., in the form of VIA contacts, corresponding to source contacts 132in FIG. 1 ) in core array regions 206A and 206B. For example, sourcecontacts 215 may be evenly distributed in core array region 206A or206B. 3D memory device 200 can include backside source lines 209 (e.g.,in the form of a source line mesh, corresponding to redistribution layer136 in FIG. 1 ) electrically connecting multiple source contacts 215. Itis understood that in some examples, multiple source VIA contacts may bereplaced by one or more source wall-shaped contacts, i.e., interconnectlines. In some embodiments, 3D memory device 200 further includespad-out contacts 213 (e.g., corresponding to contact pad 140, contact144, and peripheral contact 148 in FIG. 1 ) in staircase region 204 forpad-out and includes N-well pick up contacts 211 (e.g., corresponding tocontact 142 and peripheral contact 146 in FIG. 1 ) in staircase region204 and core array regions 206A and 206B. It is further understood thatthe layout of pad-out contacts 213 and N-well pick up contacts 211 isnot limited to the example in FIG. 2B and may include any suitablelayouts depending on the design of the 3D memory device, such as thespecification (e.g., voltage and resistance) of the electricalperformance. In one example, additional pad-out contacts 213 may beadded outside of the memory stack.

FIGS. 3A-3M illustrate a fabrication process for forming an exemplary 3Dmemory device with a backside source contact, according to someembodiments of the present disclosure. FIGS. 4A and 4B illustrate aflowchart of a method 400 for forming an exemplary 3D memory device witha backside source contact, according to some embodiments of the presentdisclosure. Examples of the 3D memory device depicted in FIGS. 3A-3M,4A, and 4B include 3D memory device 100 depicted in FIG. 1 . FIGS.3A-3M, 4A, and 4B will be described together. It is understood that theoperations shown in method 400 are not exhaustive and that otheroperations can be performed as well before, after, or between any of theillustrated operations. Further, some of the operations may be performedsimultaneously, or in a different order than shown in FIGS. 4A and 4B.

Referring to FIG. 4A, method 400 starts at operation 402, in which aperipheral circuit is formed on a first substrate. The first substratecan be a silicon substrate. As illustrated in FIG. 3I, a plurality oftransistors are formed on a silicon substrate 350 using a plurality ofprocesses including, but not limited to, photolithography, etching, thinfilm deposition, thermal growth, implantation, chemical mechanicalpolishing (CMP), and any other suitable processes. In some embodiments,doped regions (not shown) are formed in silicon substrate 350 by ionimplantation and/or thermal diffusion, which function, for example, assource regions and/or drain regions of the transistors. In someembodiments, isolation regions (e.g., STIs) are also formed in siliconsubstrate 350 by wet etching and/or dry etching and thin filmdeposition. The transistors can form peripheral circuits 352 on siliconsubstrate 350.

As illustrated in FIG. 3I, a bonding layer 348 is formed aboveperipheral circuits 352. Bonding layer 348 includes bonding contactselectrically connected to peripheral circuits 352. To form bonding layer348, an ILD layer is deposited using one or more thin film depositionprocesses, such as chemical vapor deposition (CVD), physical vapordeposition (PVD), atomic layer deposition (ALD), or any combinationthereof, and the bonding contacts are formed through the ILD layer usingwet etching and/or dry etching, e.g., ME, followed by one or more thinfilm deposition processes, such as ALD, CVD, PVD, any other suitableprocesses, or any combination thereof.

Method 400 proceeds to operation 404, as illustrated in FIG. 4A, inwhich a portion of a second substrate is doped with an N-type dopant toform a second semiconductor layer. The second substrate can be a P-typesilicon substrate. In some embodiments, the first side (e.g., the frontside at which semiconductor devices are formed) of the second substrateis doped to form an N-well. As illustrated in FIG. 3A, an N-type dopedsemiconductor layer 304 is formed on a silicon substrate 302. N-typedoped semiconductor layer 304 can include an N-well in a P-type siliconsubstrate 302 and include single crystalline silicon. N-type dopedsemiconductor layer 304 can be formed by doping N-type dopant(s), suchas P or As, into P-type silicon substrate 302 using ion implantationand/or thermal diffusion.

Method 400 proceeds to operation 406, as illustrated in FIG. 4A, inwhich a sacrificial layer above the second semiconductor layer and adielectric stack on the sacrificial layer are subsequently formed. Thedielectric stack can include interleaved stack sacrificial layers andstack dielectric layers. In some embodiments, to subsequently form thesacrificial layer and the dielectric stack, polysilicon is deposited onthe second semiconductor layer to form the sacrificial layer, and stackdielectric layers and stack sacrificial layers are alternatinglydeposited on the sacrificial layer to form the dielectric stack.

As illustrated in FIG. 3A, a sacrificial layer 306 is formed on N-typedoped semiconductor layer 304. Sacrificial layer 306 can be formed bydepositing polysilicon or any other suitable sacrificial material (e.g.,carbon) that can be later selectively removed using one or more thinfilm deposition processes including, but not limited to, CVD, PVD, ALD,or any combination thereof. In some embodiments, a pad oxide layer 305is formed between sacrificial layer 306 and N-type doped semiconductorlayer 304 by depositing dielectric materials, such as silicon oxide, orthermal oxidation, on silicon substrate 302 prior to the formation ofN-type doped semiconductor layer 304.

As illustrated in FIG. 3A, a dielectric stack 308 including a pluralitypairs of a first dielectric layer (referred to herein as “stacksacrificial layer” 312) and a second dielectric layer (referred toherein as “stack dielectric layers” 310, together referred to herein as“dielectric layer pairs”) is formed on sacrificial layer 306. Dielectricstack 308 includes interleaved stack sacrificial layers 312 and stackdielectric layers 310, according to some embodiments. Stack dielectriclayers 310 and stack sacrificial layers 312 can be alternativelydeposited on sacrificial layer 306 above silicon substrate 302 to formdielectric stack 308. In some embodiments, each stack dielectric layer310 includes a layer of silicon oxide, and each stack sacrificial layer312 includes a layer of silicon nitride. Dielectric stack 308 can beformed by one or more thin film deposition processes including, but notlimited to, CVD, PVD, ALD, or any combination thereof. As illustrated inFIG. 3A, a staircase structure can be formed on the edge of dielectricstack 308. The staircase structure can be formed by performing aplurality of so-called “trim-etch”cycles to the dielectric layer pairsof dielectric stack 308 toward silicon substrate 302. Due to therepeated trim-etch cycles applied to the dielectric layer pairs ofdielectric stack 308, dielectric stack 308 can have one or more tiltededges and a top dielectric layer pair shorter than the bottom one, asshown in FIG. 3A.

Method 400 proceeds to operation 408, as illustrated in FIG. 4A, inwhich a channel structure extending vertically through the dielectricstack and the sacrificial layer into the second semiconductor layer isformed. In some embodiments, to form the channel structure, a channelhole extending vertically through the dielectric stack and thesacrificial layer into the second semiconductor layer is formed, amemory film and a semiconductor channel are subsequently formed over asidewall of the channel hole, and a channel plug is formed above and incontact with the semiconductor channel.

As illustrated in FIG. 3A, a channel hole is an opening extendingvertically through dielectric stack 308 and sacrificial layer 306 intoN-type doped semiconductor layer 304. In some embodiments, a pluralityof openings are formed, such that each opening becomes the location forgrowing an individual channel structure 314 in the later process. Insome embodiments, fabrication processes for forming the channel hole ofchannel structure 314 include wet etching and/or dry etching, such asdeep-ion reactive etching (DRIE). In some embodiments, the channel holeof channel structure 314 extends further through the top portion ofN-type doped semiconductor layer 304. The etching process throughdielectric stack 308 and sacrificial layer 306 may continue to etch partof N-type doped semiconductor layer 304. In some embodiments, a separateetching process is used to etch part of N-type doped semiconductor layer304 after etching through dielectric stack 308 and sacrificial layer306.

As illustrated in FIG. 3A, a memory film 316 (including a blockinglayer, a storage layer, and a tunneling layer) and a semiconductorchannel 318 are subsequently formed in this order along sidewalls andthe bottom surface of the channel hole. In some embodiments, memory film316 is first deposited along the sidewalls and bottom surface of thechannel hole, and semiconductor channel 318 is then deposited overmemory film 316. The blocking layer, storage layer, and tunneling layercan be subsequently deposited in this order using one or more thin filmdeposition processes, such as ALD, CVD, PVD, any other suitableprocesses, or any combination thereof, to form memory film 316.Semiconductor channel 318 can then be formed by depositing asemiconductor material, such as polysilicon, over the tunneling layer ofmemory film 316 using one or more thin film deposition processes, suchas ALD, CVD, PVD, any other suitable processes, or any combinationthereof. In some embodiments, a first silicon oxide layer, a siliconnitride layer, a second silicon oxide layer, and a polysilicon layer (a“SONO” structure) are subsequently deposited to form memory film 316 andsemiconductor channel 318.

As illustrated in FIG. 3A, a capping layer is formed in the channel holeand over semiconductor channel 318 to completely or partially fill thechannel hole (e.g., without or with an air gap). The capping layer canbe formed by depositing a dielectric material, such as silicon oxide,using one or more thin film deposition processes, such as ALD, CVD, PVD,any other suitable processes, or any combination thereof. A channel plugthen can be formed in the top portion of the channel hole. In someembodiments, parts of memory film 316, semiconductor channel 318, andthe capping layer that are on the top surface of dielectric stack 308are removed and planarized by CMP, wet etching, and/or dry etching. Arecess then can be formed in the top portion of the channel hole by wetetching and/or drying etching parts of semiconductor channel 318 and thecapping layer in the top portion of the channel hole. The channel plugthen can be formed by depositing semiconductor materials, such aspolysilicon, into the recess by one or more thin film depositionprocesses, such as CVD, PVD, ALD, or any combination thereof. Channelstructure 314 is thereby formed through dielectric stack 308 andsacrificial layer 306 into N-type doped semiconductor layer 304.

Method 400 proceeds to operation 410, as illustrated in FIG. 4A, inwhich the sacrificial layer is replaced with an N-type dopedsemiconductor layer to form the first semiconductor layer. In someembodiments, to replace the sacrificial layer with the firstsemiconductor layer, an opening extending vertically through thedielectric stack is formed to expose part of the sacrificial layer, thesacrificial layer is etched through the opening to form a cavity, andN-type doped polysilicon is deposited into the cavity through theopening to form the first semiconductor layer.

As illustrated in FIG. 3A, a slit 320 is an opening that extendsvertically through dielectric stack 308 and exposes part of sacrificiallayer 306. In some embodiments, fabrication processes for forming slit320 include wet etching and/or dry etching, such as DRIE. In someembodiments, slit 320 extends further into the top portion ofsacrificial layer 306. The etching process through dielectric stack 308may not stop at the top surface of sacrificial layer 306 and maycontinue to etch part of sacrificial layer 306.

As illustrated in FIG. 3B, sacrificial layer 306 (shown in FIG. 3A) isremoved by wet etching and/or dry etching to form a cavity 322. In someembodiments, sacrificial layer 306 includes polysilicon, which can beetched by applying tetramethylammonium hydroxide (TMAH) etchant throughslit 320, which can be stopped by pad oxide layer 305 betweensacrificial layer 306 and N-type doped semiconductor layer 304. That is,the removal of sacrificial layer 306 does not affect N-type dopedsemiconductor layer 304, according to some embodiments. In someembodiments, prior to the removal of sacrificial layer 306, a spacer 324is formed along the sidewall of slit 320. Spacer 324 can be formed bydepositing dielectric materials, such as silicon nitride, silicon oxide,and silicon nitride, into slit 320 using one or more thin filmdeposition processes, such as CVD, PVD, ALD, or any combination thereof.

As illustrated in FIG. 3C, part of memory film 316 of channel structure314 exposed in cavity 322 is removed to expose part of semiconductorchannel 318 of channel structure 314 abutting cavity 322. In someembodiments, parts of the blocking layer (e.g., including siliconoxide), storage layer (e.g., including silicon nitride), and tunnelinglayer (e.g., including silicon oxide) are etched by applying etchantsthrough slit 320 and cavity 322, for example, phosphoric acid foretching silicon nitride and hydrofluoric acid for etching silicon oxide.The etching can be stopped by semiconductor channel 318 of channelstructure 314. Spacer 324 including dielectric materials (shown in FIG.3B) can also protect dielectric stack 308 from the etching of memoryfilm 316 and can be removed by the etchants in the same step as removingpart of memory film 316. Similarly, pad oxide layer 305 (shown in FIG.3B) on N-type doped semiconductor layer 304 can be removed as well bythe same step as removing part of memory film 316.

As illustrated in FIG. 3D, an N-type doped semiconductor layer 326 isformed above and in contact with N-type doped semiconductor layer 304.In some embodiments, N-type doped semiconductor layer 326 is formed bydepositing polysilicon into cavity 322 (shown in FIG. 3C) through slit320 using one or more thin film deposition processes, such as CVD, PVD,ALD, or any combination thereof. In some embodiments, N-type dopedsemiconductor layer 326 is formed by selectively filling cavity 322 withpolysilicon epitaxially grown from the exposed part of semiconductorchannel 318 (including polysilicon). The fabrication processes forepitaxially growing N-type doped semiconductor layer 326 can includepre-cleaning cavity 322 followed by, for example, vapor-phase epitaxy(VPE), liquid-phase epitaxy (LPE), molecular-beam epitaxy (MPE), or anycombinations thereof. In some embodiments, in-situ doping of N-typedopants, such as P or As, is performed when depositing or epitaxiallygrowing polysilicon to form an N-type doped polysilicon layer as N-typedoped semiconductor layer 326. N-type doped semiconductor layer 326 canfill cavity 322 to be in contact with the exposed part of semiconductorchannel 318 of channel structure 314.

Method 400 proceeds to operation 412, as illustrated in FIG. 4A, inwhich the dielectric stack is replaced with a memory stack, for example,using the so-called “gate replacement” process, such that the channelstructure extends vertically through the memory stack and the firstsemiconductor layer into the second semiconductor layer. In someembodiments, to replace the dielectric stack with the memory stack, thestack sacrificial layers are replaced with stack conductive layersthrough the opening. In some embodiments, the memory stack includesinterleaved stack conductive layers and stack dielectric layers.

As illustrated in FIG. 3E, stack sacrificial layers 312 (shown in FIG.3A) are replaced with stack conductive layers 328, and a memory stack330 including interleaved stack conductive layers 328 and stackdielectric layers 310 is thereby formed, replacing dielectric stack 308(shown in FIG. 3A). In some embodiments, lateral recesses (not shown)are first formed by removing stack sacrificial layers 312 through slit320. In some embodiments, stack sacrificial layers 312 are removed byapplying etchants through slit 320, creating the lateral recessesinterleaved between stack dielectric layers 310. The etchants caninclude any suitable etchants that etch stack sacrificial layers 312selective to stack dielectric layers 310. As illustrated in FIG. 3E,stack conductive layers 328 (including gate electrodes and adhesivelayers) are deposited into the lateral recesses through slit 320. Insome embodiments, a gate dielectric layer 332 is deposited into thelateral recesses prior to stack conductive layers 328, such that stackconductive layers 328 are deposited on the gate dielectric layer. Stackconductive layers 328, such as metal layers, can be deposited using oneor more thin film deposition processes, such as ALD, CVD, PVD, any othersuitable processes, or any combination thereof. In some embodiments,gate dielectric layer 332, such as a high-k dielectric layer, is formedalong the sidewall and at the bottom of slit 320 as well.

Method 400 proceeds to operation 414, as illustrated in FIG. 4B, inwhich an insulating structure extending vertically through the memorystack is formed. In some embodiments, to form the insulating structure,after forming the memory stack, one or more dielectric materials aredeposited into the opening to fill the opening. As illustrated in FIG.3F, an insulating structure 336 extending vertically through memorystack 330 is formed, stopping on the top surface of N-type dopedsemiconductor layer 326. Insulating structure 336 can be formed bydepositing one or more dielectric materials, such as silicon oxide, intoslit 320 to fully or partially fill slit 320 (with or without an airgap) using one or more thin film deposition processes, such as ALD, CVD,PVD, any other suitable processes, or any combination thereof. In someembodiments, insulating structure 336 includes gate dielectric layer 332(e.g., including high-k dielectrics) and a dielectric capping layer 334(e.g., including silicon oxide).

As illustrated in FIG. 3G, after the formation of insulating structure336, local contacts, including channel local contacts 344 and word linelocal contacts 342, and peripheral contacts 338 and 340 are formed. Alocal dielectric layer can be formed on memory stack 330 by depositingdielectric materials, such as silicon oxide or silicon nitride, usingone or more thin film deposition processes, such as CVD, PVD, ALD, orany combination thereof, on top of memory stack 330. Channel localcontacts 344, word line local contacts 342, and peripheral contacts 338and 340 can be formed by etching contact openings through the localdielectric layer (and any other ILD layers) using wet etching and/or dryetching, e.g., ME, followed by filling the contact openings withconductive materials using one or more thin film deposition processes,such as ALD, CVD, PVD, any other suitable processes, or any combinationthereof.

As illustrated in FIG. 3H, a bonding layer 346 is formed above channellocal contacts 344, word line local contacts 342, and peripheralcontacts 338 and 340. Bonding layer 346 includes bonding contactselectrically connected to channel local contacts 344, word line localcontacts 342, and peripheral contacts 338 and 340. To form bonding layer346, an ILD layer is deposited using one or more thin film depositionprocesses, such as CVD, PVD, ALD, or any combination thereof, and thebonding contacts are formed through the ILD layer using wet etchingand/or dry etching, e.g., RIE, followed by one or more thin filmdeposition processes, such as ALD, CVD, PVD, any other suitableprocesses, or any combination thereof.

Method 400 proceeds to operation 416, as illustrated in FIG. 4B, inwhich the first substrate and the second substrate are bonded in aface-to-face manner, such that the memory stack is above the peripheralcircuit. The bonding can be hybrid bonding. As illustrated in FIG. 3I,silicon substrate 302 and components formed thereon (e.g., memory stack330 and channel structures 314 formed therethrough) are flipped upsidedown. Bonding layer 346 facing down is bonded with bonding layer 348facing up, i.e., in a face-to-face manner, thereby forming a bondinginterface 354 between silicon substrates 302 and 350, according to someembodiments. In some embodiments, a treatment process, e.g., a plasmatreatment, a wet treatment, and/or a thermal treatment, is applied tothe bonding surfaces prior to the bonding. After the bonding, thebonding contacts in bonding layer 346 and the bonding contacts inbonding layer 348 are aligned and in contact with one another, such thatmemory stack 330 and channel structures 314 formed therethrough can beelectrically connected to peripheral circuits 352 and are aboveperipheral circuits 352.

Method 400 proceeds to operation 418, as illustrated in FIG. 4B, inwhich the second substrate is thinned to expose the second semiconductorlayer. The thinning is performed from the second side (e.g., thebackside) opposite to the first side of the second substrate. Asillustrated in FIG. 3J, silicon substrate 302 (shown in FIG. 3I) isthinned from the backside to expose N-type doped semiconductor layer304. Silicon substrate 302 can be thinned using CMP, grinding, dryetching, and/or wet etching. In some embodiments, the CMP process isperformed to thin silicon substrate 302 until reaching the top surfaceof N-type doped semiconductor layer 304.

Method 400 proceeds to operation 420, as illustrated in FIG. 4B, inwhich a source contact is formed above the memory stack and in contactwith the second semiconductor layer. In some embodiments, the sourcecontact is formed at the second side (e.g., the backside) opposite tothe first side of the second substrate (e.g., the second semiconductorlayer after thinning). In some embodiments, the source contact isaligned with the insulating structure.

As illustrated in FIG. 3K, one or more ILD layers 356 are formed onN-type doped semiconductor layer 304. ILD layers 356 can be formed bydepositing dielectric materials on the top surface of N-type dopedsemiconductor layer 304 using one or more thin film depositionprocesses, such as ALD, CVD, PVD, any other suitable processes, or anycombination thereof. As illustrated in FIG. 3K, a source contact opening358 is formed through ILD layers 356 into N-type doped semiconductorlayer 304. In some embodiments, source contact opening 358 is formedusing wet etching and/or dry etching, such as ME. In some embodiments,source contact opening 358 extends further into the top portion ofN-type doped semiconductor layer 304. The etching process through ILDlayers 356 may continue to etch part of N-type doped semiconductor layer304. In some embodiments, a separate etching process is used to etchpart of N-type doped semiconductor layer 304 after etching through ILDlayers 356. In some embodiments, source contact opening 358 is patternedusing lithography to be aligned with insulating structure 336 atopposite sides of N-type doped semiconductor layer 304.

As illustrated in FIG. 3L, a source contact 364 is formed in sourcecontact opening 358 (shown in FIG. 3K) at the backside of N-type dopedsemiconductor layer 304. Source contact 364 is above memory stack 330and in contact with N-type doped semiconductor layer 304, according tosome embodiments. In some embodiments, one or more conductive materialsare deposited into source contact opening 358 using one or more thinfilm deposition processes, such as ALD, CVD, PVD, any other suitableprocesses, or any combination thereof, to fill source contact opening358 with an adhesive layer (e.g., TiN) and a conductor layer (e.g., W).A planarization process, such as CMP, then can be performed to removethe excess conductive materials, such that the top surface of sourcecontact 364 is flush with the top surface of ILD layers 356. In someembodiments, as source contact opening 358 is aligned with insulatingstructure 336, backside source contact 364 is aligned with insulatingstructure 336 as well.

Method 400 proceeds to operation 422, as illustrated in FIG. 4B, inwhich an interconnect layer is formed above and in contact with thesource contact. As illustrated in FIG. 3M, a redistribution layer 370 isformed above and in contact with source contact 364. In someembodiments, redistribution layer 370 is formed by depositing aconductive material, such as Al, on the top surfaces of N-type dopedsemiconductor layer 304 and source contact 364 using one or more thinfilm deposition processes, such as ALD, CVD, PVD, any other suitableprocesses, or any combination thereof. As illustrated in FIG. 3M, apassivation layer 372 is formed on redistribution layer 370. In someembodiments, passivation layer 372 is formed by depositing a dielectricmaterial, such as silicon nitride, using one or more thin filmdeposition processes, such as ALD, CVD, PVD, any other suitableprocesses, or any combination thereof. An interconnect layer 376including ILD layers 356, redistribution layer 370, and passivationlayer 372 is thereby formed, according to some embodiments.

Method 400 proceeds to operation 424, as illustrated in FIG. 4B, inwhich a contact is formed through the second semiconductor layer and incontact with the interconnect layer, such that the first semiconductorlayer is electrically connected to the contact through the secondsemiconductor layer, the source contact, and the interconnect layer. Asillustrated in FIG. 3K, contact openings 360 and 361 each extendingthrough ILD layers 356 and N-type doped semiconductor layer 304 areformed. Contact openings 360 and 361 and source contact opening 358 canbe formed using the same etching process to reduce the number of etchingprocesses. In some embodiments, contact openings 360 and 361 are formedusing wet etching and/or dry etching, such as RIE, through ILD layers356 and N-type doped semiconductor layer 304. In some embodiments,contact openings 360 and 361 are patterned using lithography to bealigned with peripheral contacts 338 and 340, respectively. The etchingof contact openings 360 and 361 can stop at the upper ends of peripheralcontacts 338 and 340 to expose peripheral contacts 338 and 340. Asillustrated in FIG. 3K, a spacer 362 is formed along the sidewalls ofcontact openings 360 and 361 to electrically isolate N-type dopedsemiconductor layer 304 using one or more thin film depositionprocesses, such as ALD, CVD, PVD, any other suitable processes, or anycombination thereof.

As illustrated in FIG. 3L, contacts 366 and 368 are formed in contactopenings 360 and 361, respectively (shown in FIG. 3K) at the backside ofN-type doped semiconductor layer 304. Contacts 366 and 368 extendvertically through ILD layers 356 and N-type doped semiconductor layer304, according to some embodiments. Contacts 366 and 368 and sourcecontact 364 can be formed using the same deposition process to reducethe number of deposition processes. In some embodiments, one or moreconductive materials are deposited into contact openings 360 and 361using one or more thin film deposition processes, such as ALD, CVD, PVD,any other suitable processes, or any combination thereof, to fillcontact openings 360 and 361 with an adhesive layer (e.g., TiN) and aconductor layer (e.g., W). A planarization process, such as CMP, thencan be performed to remove the excess conductive materials, such thatthe top surfaces of contacts 366 and 368 are flush with the top surfaceof ILD layers 356. In some embodiments, as contact openings 360 and 361are aligned with peripheral contacts 338 and 340, respectively, contacts366 and 368 are above and in contact with peripheral contacts 338 and340, respectively, as well.

As illustrated in FIG. 3M, redistribution layer 370 is also formed aboveand in contact with contact 366. As a result, N-type doped semiconductorlayer 326 can be electrically connected to peripheral contact 338through N-type doped semiconductor layer 304, source contact 364,redistribution layer 370 of interconnect layer 376, and contact 366. Insome embodiments, N-type doped semiconductor layers 326 and 304 areelectrically connected to peripheral circuits 352 through source contact364, interconnect layer 376, contact 366, peripheral contact 338 andbonding layers 346 and 348.

As illustrated in FIG. 3M, a contact pad 374 is formed above and incontact with contact 368. In some embodiments, part of passivation layer372 covering contact 368 is removed by wet etching and dry etching toexpose part of redistribution layer 370 underneath to form contact pad374. As a result, contact pad 374 for pad-out can be electricallyconnected to peripheral circuits 352 through contact 368, peripheralcontact 340, and bonding layers 346 and 348.

According to one aspect of the present disclosure, a method for forminga 3D memory device is disclosed. A sacrificial layer above a secondsemiconductor layer at a first side of a substrate and a dielectricstack on the sacrificial layer are subsequently formed. A channelstructure extending vertically through the dielectric stack and thesacrificial layer into the second semiconductor layer is formed. Thesacrificial layer is replaced with a first semiconductor layer incontact with the second semiconductor layer. The dielectric stack isreplaced with a memory stack, such that the channel structure extendsvertically through the memory stack and the first semiconductor layerinto the second semiconductor layer. A source contact is formed at asecond side opposite to the first side of the substrate to be in contactwith the second semiconductor layer.

In some embodiments, prior to forming the sacrificial layer, a portionof the substrate is doped, at the first side, with an N-type dopant toform the second semiconductor layer.

In some embodiments, to replace the sacrificial layer with the firstsemiconductor layer, an opening extending vertically through thedielectric stack is formed to expose part of the sacrificial layer, thesacrificial layer is etched through the opening to form a cavity, andN-type doped polysilicon is deposited into the cavity through theopening to form the first semiconductor layer.

In some embodiments, to subsequently form the sacrificial layer and thedielectric stack, polysilicon is deposited on the second semiconductorlayer to form the sacrificial layer, and stack dielectric layers andstack sacrificial layers are alternatingly deposited on the sacrificiallayer to form the dielectric stack.

In some embodiments, to replace the dielectric stack with the memorystack, the stack sacrificial layers are replaced with stack conductivelayers through the opening.

In some embodiments, after forming the memory stack, one or moredielectric materials are deposited into the opening to form aninsulating structure extending vertically through the memory stack.

In some embodiments, the source contact is aligned with the insulatingstructure.

In some embodiments, prior to forming the source contact, the substrateis tinned thinning, from the second side, to expose the secondsemiconductor layer.

In some embodiments, an interconnect layer is formed above andelectrically connected to the source contact.

In some embodiments, a contact through the second semiconductor layerand in contact with the interconnect layer is formed, such that thefirst semiconductor layer is electrically connected to the contactthrough the second semiconductor layer, the source contact, and theinterconnect layer.

According to another aspect of the present disclosure, a method forforming a 3D memory device is disclosed. A channel structure extendingvertically through a memory stack into an N-type doped semiconductorlayer at a first side of a substrate is formed. The memory stackincludes interleaved stack conductive layers and stack dielectriclayers. An insulating structure is formed in an opening extendingvertically through the memory stack. A source contact is formed at asecond side opposite to the first side of the substrate to be in contactwith the N-type doped semiconductor layer and aligned with theinsulating structure.

In some embodiments, to form the channel structure, a portion of thesubstrate is doped, at the first side, with an N-type dopant to form asecond N-type doped semiconductor layer, a sacrificial layer above thesecond N-type doped semiconductor layer and a dielectric stack on thesacrificial layer are subsequently forming, the dielectric layerincluding interleaved stack sacrificial layers and the stack dielectriclayers, the channel structure extending vertically through thedielectric stack and the sacrificial layer into the second N-type dopedsemiconductor layer is formed, and the sacrificial layer is replacedwith a first N-type doped semiconductor layer through the opening.

In some embodiments, to form the channel structure, the stacksacrificial layers are replaced with the stack conductive layers to formthe memory stack.

In some embodiments, to form the insulating structure, after replacingthe stack sacrificial layers with the stack conductive layers, theopening is filled with one or more dielectric materials.

In some embodiments, prior to forming the source contact, the substrateis thinned, from the second side to expose the second N-type dopedsemiconductor layer.

According to still another aspect of the present disclosure, a methodfor forming a 3D memory device is disclosed. A peripheral circuit isformed on a first substrate. A channel structure extending verticallythrough a memory stack and a first semiconductor layer into a secondsemiconductor layer on a second substrate is formed. The first substrateand the second substrate are bonded in a face-to-face manner, such thatthe memory stack is above the peripheral circuit. The second substrateis thinned to expose the second semiconductor layer. A source contact isformed above the memory stack and in contact with the secondsemiconductor layer.

In some embodiments, to form the channel structure, a portion of thesecond substrate is doped with an N-type dopant to form a secondsemiconductor layer, a sacrificial layer above the second semiconductorlayer and a dielectric stack on the sacrificial layer are subsequentlyforming, the channel structure extending vertically through thedielectric stack and the sacrificial layer into the second semiconductorlayer is formed, and the sacrificial layer is replaced with an N-typedoped semiconductor layer through the opening to form the firstsemiconductor layer.

In some embodiments, to form the channel structure further, thedielectric stack is replaced with the memory stack.

In some embodiments, prior to bonding the first substrate and the secondsubstrate, an insulating structure extending vertically through thememory stack is formed. The source contact is aligned with theinsulating structure, according to some embodiments.

In some embodiments, an interconnect layer is formed above and incontact with the source contact.

In some embodiments, a contact through the second semiconductor layerand in contact with the interconnect layer is formed, such that thefirst semiconductor layer is electrically connected to the contactthrough the second semiconductor layer, the source contact, and theinterconnect layer.

The foregoing description of the specific embodiments will so reveal thegeneral nature of the present disclosure that others can, by applyingknowledge within the skill of the art, readily modify and/or adapt forvarious applications such specific embodiments, without undueexperimentation, without departing from the general concept of thepresent disclosure. Therefore, such adaptations and modifications areintended to be within the meaning and range of equivalents of thedisclosed embodiments, based on the teaching and guidance presentedherein. It is to be understood that the phraseology or terminologyherein is for the purpose of description and not of limitation, suchthat the terminology or phraseology of the present specification is tobe interpreted by the skilled artisan in light of the teachings andguidance.

Embodiments of the present disclosure have been described above with theaid of functional building blocks illustrating the implementation ofspecified functions and relationships thereof. The boundaries of thesefunctional building blocks have been arbitrarily defined herein for theconvenience of the description. Alternate boundaries can be defined solong as the specified functions and relationships thereof areappropriately performed.

The Summary and Abstract sections may set forth one or more but not allexemplary embodiments of the present disclosure as contemplated by theinventor(s), and thus, are not intended to limit the present disclosureand the appended claims in any way.

The breadth and scope of the present disclosure should not be limited byany of the above-described exemplary embodiments, but should be definedonly in accordance with the following claims and their equivalents.

What is claimed is:
 1. A method for forming a three-dimensional (3D)memory device, comprising: forming a sacrificial layer above a secondsemiconductor layer at a first side of a substrate and a dielectricstack on the sacrificial layer; forming a channel structure extendingvertically through the dielectric stack and the sacrificial layer intothe second semiconductor layer; replacing the sacrificial layer with afirst semiconductor layer in contact with the second semiconductorlayer; replacing the dielectric stack with a memory stack, such that thechannel structure extends vertically through the memory stack and thefirst semiconductor layer into the second semiconductor layer; andforming a source contact at a second side to be in contact with thesecond semiconductor layer, a portion of the source contact being buriedinto and surrounded by the second semiconductor layer, and the sourcecontact being electrically connected with the first semiconductor layerand the second semiconductor layer.
 2. The method of claim 1, furthercomprising prior to forming the sacrificial layer, doping, at the firstside, a portion of the substrate with an N-type dopant to form thesecond semiconductor layer.
 3. The method of claim 1, wherein replacingthe sacrificial layer with the first semiconductor layer comprises:forming an opening extending vertically through the dielectric stack toexpose part of the sacrificial layer; etching the sacrificial layerthrough the opening to form a cavity; and depositing N-type dopedpolysilicon into the cavity through the opening to form the firstsemiconductor layer.
 4. The method of claim 3, wherein subsequentlyforming the sacrificial layer and the dielectric stack comprises:depositing polysilicon on the second semiconductor layer to form thesacrificial layer; and alternatingly depositing stack dielectric layersand stack sacrificial layers on the sacrificial layer to form thedielectric stack.
 5. The method of claim 4, wherein replacing thedielectric stack with the memory stack comprises replacing the stacksacrificial layers with stack conductive layers through the opening. 6.The method of claim 3, further comprising after forming the memorystack, depositing one or more dielectric materials into the opening toform an insulating structure extending vertically through the memorystack.
 7. The method of claim 6, wherein the source contact is alignedwith the insulating structure.
 8. The method of claim 1, furthercomprising prior to forming the source contact, thinning, from thesecond side, the substrate to expose the second semiconductor layer. 9.The method of claim 1, further comprising forming an interconnect layerabove and electrically connected to the source contact.
 10. The methodof claim 9, further comprising forming a contact through the secondsemiconductor layer and in contact with the interconnect layer, suchthat the first semiconductor layer is electrically connected to thecontact through the second semiconductor layer, the source contact, andthe interconnect layer.
 11. The method of claim 1, wherein the secondsemiconductor layer and a dielectric layer are arranged on a sidewall ofthe source contact.
 12. A method for forming a three-dimensional (3D)memory device, comprising: forming a channel structure extendingvertically through a memory stack into an N-type doped semiconductorlayer at a first side of a substrate, wherein the memory stack comprisesinterleaved stack conductive layers and stack dielectric layers; formingan insulating structure in an opening extending vertically through thememory stack; and forming a source contact at a second side to be incontact with the N-type doped semiconductor layer and aligned with theinsulating structure, the source contact being electrically connectedwith a contact that penetrates the N-type doped semiconductor layer. 13.The method of claim 12, wherein forming the channel structure comprises:doping at the first side, a portion of the substrate with an N-typedopant to form a second N-type doped semiconductor layer; subsequentlyforming a sacrificial layer above the second N-type doped semiconductorlayer and a dielectric stack on the sacrificial layer, wherein thedielectric stack comprises interleaved stack sacrificial layers and thestack dielectric layers; forming the channel structure extendingvertically through the dielectric stack and the sacrificial layer intothe second N-type doped semiconductor layer, the N-type dopedsemiconductor layer comprising the second N-type doped semiconductorlayer; and replacing the sacrificial layer with a first N-type dopedsemiconductor layer through the opening.
 14. The method of claim 13,wherein forming the channel structure further comprises replacing thestack sacrificial layers with the stack conductive layers to form thememory stack.
 15. The method of claim 14, wherein forming the insulatingstructure comprises after replacing the stack sacrificial layers withthe stack conductive layers, filling the opening with one or moredielectric materials.
 16. The method of claim 13, further comprisingprior to forming the source contact, thinning, from the second side, thesubstrate to expose the second N-type doped semiconductor layer.
 17. Amethod for forming a three-dimensional (3D) memory device, comprising:forming a peripheral circuit on a first substrate; forming a channelstructure extending vertically through a memory stack and a firstsemiconductor layer into a second semiconductor layer on a secondsubstrate; forming an insulating structure extending vertically throughthe memory stack; after forming the insulating structure, bonding thefirst substrate and the second substrate in a face-to-face manner, suchthat the memory stack is above the peripheral circuit; thinning thesecond substrate to expose the second semiconductor layer; and forming asource contact above the memory stack and in contact with the secondsemiconductor layer, wherein the source contact is aligned with theinsulating structure.
 18. The method of claim 17, wherein forming thechannel structure comprises: doping a portion of the second substratewith an N-type dopant to form the second semiconductor layer;subsequently forming a sacrificial layer above the second semiconductorlayer and a dielectric stack on the sacrificial layer; forming thechannel structure extending vertically through the dielectric stack andthe sacrificial layer into the second semiconductor layer; and replacingthe sacrificial layer with an N-type doped semiconductor layer to formthe first semiconductor layer.
 19. The method of claim 17, furthercomprising forming an interconnect layer above and in contact with thesource contact.
 20. The method of claim 19, further comprising forming acontact through the second semiconductor layer and in contact with theinterconnect layer, such that the first semiconductor layer iselectrically connected to the contact through the second semiconductorlayer, the source contact, and the interconnect layer.